Process of fractionating mineral oils



Patented May 30,1939

UNITED STATES PATENT OFFICE PROCESS OF FRAfifiigNATING MINERAL NoDrawing.

Application August 27, 1938,

Serial No. 227,174

14 Claims.

ture at which a portion thereof is solidified and separating thesolidified portion from the liquid .applied for separating various waxysubstances from mineral oils, such as lubricating oils and fuel oils,and the like, to lower their pour points and/or their cloud points. Itmay, further, be applied to the manufacture of lubricating oil fractionsof high viscosity index from the mam lubricating oilfractions which mayor may not contain wax; or to the concentration of constituents of fuelsfor internal combustion engines which have superior anti-detonatingproperties, 20 such as high octane gasoline-or high cetene Diesel fuel;or to the concentration of burning oils of superior burning quality.This application is a continuation-in-part of our copending applicationSerial No. 65,843, filed February 26, 1936.

The removal of wax'from mineral oil has in the past been effected bydiluting the waxy oil with a dewaxingdiluent primarily to lower theviscosity of the oil, chilling the resulting solutions to solidify thewax in a crystalline or amorphous 30 form, and separating the latterfrom the oil diluent solution by any suitable means, 'such asfiltration, cold settling, decanting, or centrifuging, depending on thenature of the wax, 'and its density. To improve the yield and lower thepour '35 point of the dewaxed oil, it has more recently been .proposedtoemploy as dewaxing diluents certain selective solvents, or mixtures ofselective solvents with solubility enhancing agents, which selectivedewaxing diluents or diluent mixtures not only reduce the viscosity ofthe oil solution but also exercise a selective solvent action betweenthe oil and the wax, whereby the wax has a reduced solubility in the oilsolution, and less oil is removed with the wax, while, less wax remains4;; dissolved in the oil. For example, a mixture of acetone and benzolhas been employed as a solvent combination for this purpose.

Similar solvent mixtures have been employed to separate hydrocarbonfractions having melting 50 points lower than that of parafiin wax byasimilar process, employing lower temperatures such as temperaturesbetween 20 and -130 C. In

such selective solvent mixtures, one function of the selective solventis to lower the solubility of I 55 the'solidified higher meltingconstituent, such as portion. The invention may, for example, be

solid wax, in the liquid phase. The selective solvents which are able tofunction in this manner are, however, generally not sum'ciently misciblewith the portion of the oil which is liquid at the dewaxing temperature,and it is often necessary 5 to add another liquid which is miscible withthe oil and with the selective solvent. The latter liquid is commonlyknown as the solubility enhancing agent. In accordance with the presentinvention we have found that petroleum nitrogen bases are excellentdiluents for fractionating processes of the type described whereinhydrocarbon mixtures are separated into portions having differentfreezing or solidification temperatures, and may be employed fordewaxing oil or for effecting a separation between hydrocarbons whichare liquid at the solidification temperature of wax. The petroleumnitrogen bases may be employed either alone as single selectivediluents, or as solubility enhancing agents in combination with otherselective solvents. By "petroleum nitrogen bases" we mean the organicheterocyclic compounds containing nitrogen in the ring which areobtained by the acid extraction of various'hydrocarbon distillatesboiling within gasoline and kerosene range; i. e., boiling between about115 C.-and- 330 0., and produced either by the straight or crackingdistillation of petroleum crude oils, shale oil, coal tar, and similarhydrocarbon 0 materials. We have found, moreover, that the petroleumheterocyclic nitrogen bases which contain heterocyclic nitrogen inaromatic rings are superior to nitrogen bases containing nitrogen in anaphthenic ring structure. For this reason, we

prefer to obtain our petroleum nitrogen bases from cracked distillates,because acid and/or solvent'extraction products from these distillatesgenerally contain upwards of about 60% aromatic nitrogen bases, whilethe. products derived 40 from straight run kerosene may contain aslittle as 15% aromatic nitrogen bases and 85% naphthenic nitrogen bases.

The concentratipn of the nitrogen bases containing heterocyclic nitrogenin cracked distillates maybe increased by mixing the charging stockprior to cracking with nitrogen gases derived from any source, andparticularly with nitrogen bases obtained by acid extraction of crudeoils or uncracked distillates. Thus, in the acid treatment of uncrackeddistillates, it is common to treat the acid sludge with a base'such asammonia to form ammonium sulfate and liberate the nitrogen bases. Theseliberated bases may be added to charging stock which is fed to crackingstills,

thereby improving the yield of cyclic compounds containing heterocyclic'nitrogen, and particularly the aromatic nitrogen bases in the crackeddistillate. Nitrogen bases derived from kerosene and similar straightrun distillates may, however, be employed. In general, however, it ispreferable to treat nitrogen bases which have been derived fromuncracked distillates with hydrochloric acid and chloroform, asdescribed by Perrin and Bailey in J. Am. Chem. Soc., vol. 55, pages 4136et seq., (Oct., 1933) to concentrate the aromatic nitrogen bases.

The petroleum nitrogen bases which are to be employed according to thepresent invention may be obtained from cracked or uncracked distillatesby any suitable extraction method employing either selective solvents oracids, or both, and it is understood that the methods described hereinare exemplary only. According to one mode of extraction, the acidsludge, which is obtained by washing a light distillate (such as crackedgasoline or'kerosene) with sulfuric acid of 83% to 97% concentration,may be neutralized with an alkaline medium, such as caustic soda orammonia, and the nitrogen bases may be separated therefrom as thesupernatant layer. If desired, the separated supernatant layer may begiven a further'extractive treatment to eliminate hydrocarbon oil.

According to another method, untreated distillate, such as raw crackeddistillate, may be treated with an excess of a comparatively strongacid, such as sulfuric or hydrochloric, to yield m acid phase, whichthen may be separated from J the distillate and neutralized as describedabove.

From 1% to 20% of acid, based on the distillate, is generallysatisfactory, although other quantities of acid may beemployed. In thecase of sulfuric acid, the concentration of the acid may range from 5%to 50%, but more dilute solutions may be employed. If so desired, theseparated aye: after neutralization with an alkaline medium may besubjected to additional treatment to separate any neutral hydrocarbonoil.

We may employ as our diluents the mixtures of nitrogen bases obtained asa result of the above described treatments or as a result of .anextraction with selective solvents. It isoften' desirable, however, to"treat these products further to concentrate their most valuableconstituents, as described below.

The products obtained from cracked distillates by extraction with acidsor other solvents may, for example, also be treated with hydrochloricacid and chloroform, or in any equivalent manner of treatment, toconcentrate the aromatic nitrogen bases, which have been found to beparticularly suitable for use as diluents for. dewaxing and for theseparation of hydrocarbons of lower melting points.

We have found moreover, that the nitrogen bases which have lowdissociation constants, i. e., those having dissociation constants lower.than

about 1x 10- are superior to those having higher dissociation constants,and when a distillate contains a large proportion of nitrogen baseshaving high dissociation constants, such as aliphatic or naphthenicamines; it is often desirable to exclude them from the diluents whichare used in the process. Various methods for concentrating the lowdissociation constant bases may be employed. For example, the-mixturesof nitrogen bases obtained according to any of the abovedescribedmethods may be further treated with weak acids.

such as ovalic or acetic and to extract therefrom above stated range maybe employed, we occasionally prefer to employ those which boil withinthe ,range of 200 C. to 300 0., since the latter have solubilitycharacteristics which are particularly suitable for our separations.

The nitrogen bases isolated by the acid treatment of cracked oruncracked distillates are believed to include substantial quantities ofcom pounds of the homologous series represented by the followingcompounds: pyridine, quinoline, and isoquinoline, although pyridine,quinoline and isoquinoline themselves may not be present in .substantialamounts. Many other types of nitrogen bases are, however, also present.Since the mixtures of nitrogen bases derived from these distillates arehighly complex, and contain a great variety of different compounds,which may vary with the source of the initial cracking material, we donot limit our invention to any theory therein expressed concerning thecomposition of the nitrogen bases to be employ .d, but'intend to includewithin the scope of our invention all nitrogen bases which are derivedfrom the above described distillates by extraction with acids.

The petroleum nitrogen bases may be employed either alone or incombination with some highly selective solvents having a low solubilityin oil such as selective solvents used for dewaxing oils. When mixedwith such'selective solvents, the

petroleum nitrogen bases act as solubility enhancing agents and exercisesome selective solvent action of their own. Among selective solventswhich may be employed in combination with petroleum nitrogen bases arethe following: Symmetrical and unsymmetrical aliphatic ketones, primary,secondary, and tertiary alcohols, aliphatic esters, aliphatic acids,hydroxy or ketoaliphatic acids, anhydrides of aliphatic acids, allpreferably containing not more than about five carbon atoms in themolecule; halogenated derivatives of oxygenated aliphatic substances;and

cyclic compounds containing oxygen or nitrogen -in the ring and theirhalogenated and substituted derivatives. Specific examples of thesesubstances are: acetone, ethyl methyl ketone, diacetone alcohol,methyl-formate, ethyl formate, methyl acetate, ethylacetate, aceticacid, butyric acid, lactic acid, acetic anhydride, methyl carbonate,p,3'-dichlorethyl ether, chlor-acetic acid, ethyl propyl and butylalcohols, quinoline, pyridine, furfural, aniline, cresylic acid,triethanolamine, and nitrobenzene. Although we have enumerated a fewspecific selective solvents which are suitable for use as diluents forour process when used in conjunction with a solubility enhancing agent,it should be noted that our invention is not limited to this smallgroupbut that the petroleum nitrogen bases may be used with any otherselective solvent which has the property of creating in the chilledhydrocarbon mixture-diluent system a'condition in which the con-"stituent having the higher solidifying tempera ficient' quantit'ypfpetroleum nitrogen bases are employed, the liquid hydrocarbons will notbe and the liquid hydrocarbons to form a homoge-. neous liquid phase atthe temperature at which the solid is. separated from the liquid,although even ture has a minimum solubility in the liquid phase. Thus,in the case of a dewaxing operation, the selective solvent lowers thesolubility of the wax in the solution of oil and diluent.

Although our invention may be practiced with all types of selectivesolvents of the type described above, we prefer to employ a selectivesolvent .which is itself a nitrogen base, and contains no alkyl sidechain or only small alkyl side chains;

i. e., alkyl side chains containing not over two carbon atoms. lectivesolvents are: pyridine, quinoline, isoquinoline, quinaldine, a picoline,p picoline, and lutidines. 'Such solvents possess a high selecutivltybetween hydrocarbons solidifying at diflerent temperatures, suchas between wax and oil, but

' often are not sufiiciently miscible with the fraction which is to berecovered in the liquid phase at the low temperatures employed. Thus, inde- 20 waxing operations, they do not dissolve enough oil at thedewaxing temperature to permit eilec-- tive dewaxing. -The addition ofpetroleum nitrogen bases obtained in the above described mannerincreases their solvent power for the liquid 25, portion of the chilledand partially solidified mixture, while preserving their selectivity.

The ratio of selective solvent to' petroleum nitrogen bases may bevaried within wide limits, and we may operate with pure petroleumnitrogen bases, or with any desired mixture of petroleum nitrogen basesand selective solvent. Suitable mixtures may, for example, consist of 50parts by volume of petroleum nitrogen bases and 50 parts of selectivesolvent, although other ratios, such as a '25/75 or 75/25 may beemployed. For most efficient dewaxing operations, it is desirable thatthe diluent mixture have a high solvent poweri'or the liquidhydrocarbons, i. e., for oil in the cas of dewaxing and a-low solventpower for hydrocarbons which are solid or semi-solid at the temperatureemployed'for dewaxing, i. e., for wax in the case of dewaxing. The lowsolubility selective solvents, of which the nitrogen bases, andparticularly quinoline and isoquinoline, are the a preferred examples,are efiective in lowering the solubility of the solid or semi-solidhydrocarbons in the liquid; phase, while the petroleum nitrogen basesare eil'ective in raising the solvent power of the s'elective solventfor liquid hydrocarbons.

when'nop troleuni nitrogen bases or an insufcompletely dissolved inthe'selective solvent, and two iquid. phases will be present inaddition, to

-the solid or semi-solid phase at the separating temperature." Whenoperating under such conditions oils having very low pour points andlower-melting fractions of high purity are often obtained, but theyields are generally low. Such a result is'often desirable when thesolidified fraction is the most valuable product, as when it is desiredto produce a parafllnic kerosene or gas oil or diesel fuels. basesslightly increases the melting pointor pour point of the liquidfraction, and'increases the yield of this fraction considerably, thisbeing desirable when :the liquid fraction is the valuable product, as indewaxing or in manufacturing gasoline oty'siiperior anti detonatingproperties. In the latter situation, it-will be advantageous to thequantity of petroleum nitrogcnbasecwhich is-required to cause thediluent Examples of these preferred'sequently by distillation.

Adding more petroleum nitrogen,

'chilled to separate addi transition between the one liquid phase andthe twoliquid phase conditions. Oil yields may be improved further byemploying higher concentrations of nitrogen bases, but the pour pointsof the treated oils are slightly higher.

The dilution ratio, 1. e., the volume ratio of initial oil to diluent ordiluent mixture is determined by the viscosity of the oil-diluentsolution at the separating temperature, and will depend upon theviscosity of the oil and of the diluent, and upon the dewaxingtemperature. For example, dilution ratios of 2:1 to 1:8 have been foundto be suitable.

As applied to the dewaxing of oils, the process may be operated, forexample, by dissolving a wax bearing oil, such as parafiinous petroleumresidues caused. to separate out in a crystalline or 'amorphous state ata lower-temperature, such as, for example, 0., 0 'C., or C., or lower,depending upon the desired pour point of the dewaxed oil and/or thedesired melting point of the wax. The separation of the solidified waxmay be carried out in any desired manner, although we have foundfiltration methods to be most suitable. centrifuging, decantation, orcold settling may, however, often be employed, especially when thespecific gravity of the selective solvent is such as to cause asufficient diiference between the densities of the oil phase and theprecipitated wax. After the separationof the wax, the dewaxing solventsmay be removed from the oil and from the wax by ordinary or vacuumdistillation,

or by any other method, such as washing with another solvent, which maybe removed subse- Aqueous solutions of methanol or ethanol have beenfound to be suitable as washing solvents. The dewaxing may be carriedout either as a continuous or a batch method.

It is desirable, but not essential, to produce a homogeneous oil-solventsystembefore' chilling the oil to precipitate the wax. To achieve this,the dewaxing diluent may be added to the oil at an elevated temperature,or the'mixture of oil and a diluent may, after mixing, be heated. It is,moreover, often advantageous to heat the mixture to a temperaturegenerally not above 150 C. and in most cases between ,C. and 110 C.before chilling to improve the filtration rate.

Filter aids may likewise be employed during the filtration. Moreover,the dewaxing may be further improved by adding a pour point reducer,such as aluminum steal-ate, cracked residues, and the like to the oil insmall quantities, generally not above 1%. 1

Under certain conditions a multiple stage process, it is desired toobtain high melting wax in the first stage, the precipitation 'of thewax may be eflected at temperatures which are the same as or'onlyslightly below normal. The oil filtrate 'may,-if desired after furtheraddition of dewaxing diluent, be further as .when a moderately high pourpoint is permissible, and/or when, in

nal quantities of wax.

addition of these It is not necessary to mix all of the components ofthe diluent mixture before dissolving them in the oil. Thus, thepetroleum nitrogen bases may be added first, and the requisite amount ofthe selective solvent or a solution of selective solvent containingpetroleum nitrogen bases may be added separately. Although it is"preferred to add the nitrogen bases to the oil prior to chilling, thepresent invention contemplates the bases at any stage, so as to bepresent .when the solid wax is separated from the oil.

The same steps may be employed in the fractionations to effectseparations between hydrocarbons which solidify at lower temperatures,the separation between the solid or semi-solid portion and the liquidportion being made at lower temperatures, e. g., between -20 C. and -130C., as is well known in the art. (See U. S. Patent Nos. 1,980,649 and2,108,629.) In these processes the more parafilnic or saturatedhydrocarbons are recovered from the solidified fraction, while the morearomatic or less saturated hydrocarbons are recovered from the liquidfraction. Such low temperature fractionations may be applied to wax-freeor to waxy oils, the wax being, in the latter case, solidified togetherwith the more parafiinic hydrocarbons. If desired, waxy oils may begiven a preliminary dewaxing treatment prior to being subjected to thelow temperature treatment.

The effect of using petroleum nitrogen bases for dewaxing may be seenfrom the following examples which are not, however, to be regarded asrestricting the scope of this specification:

Example I A waxy lubricating oil of SAE 40 grade, prepared by solventextraction of a Coalinga (San Joaquin Valley) lubricating distillate oilwith S0: in conjunction with kerosene extract had a pour point of 65 F.(A; S. T. M. Method D97--34). This oil was mixed with 50% by volume ofpetroleum nitrogen bases obtained by sulfuric acid extraction ofuntreated pressure distillate, followed by neutralization andre-extraction to release hydrocarbon oil, and finally by fractionaldistillation to isolate the fraction boiling between 243 and 262 C. Thediluted oil was chilled and filtered at 32 F., to produce an oi1 havinga pour point of 40 F.

Example II I The same oil was mixed wtih by volume of quinoline plus 30%petroleum nitrogen'bases, obtained as described in Example I. Oncarrying out a similar dewaxing at 32 F. the pour point of the' oil wasreduced to 30 F.

In both examples the dewaxing diluent was removed from the oil bywashing with methanol containing a small amount of water which wassubsequently removed from the oil by heating under vacuum.

We claim as our invention: 1. A process for separating mineral oilscontaining several hydrocarbon components having' difierentsolidification temperatures, comprising the steps of chilling said oilto a separation temperature to solidify a component thereof, andseparating said solidified component from a component having a lowersolidification temperature in the presence of separating diluentcontaining petroleum nitrogen bases separated from a mineral oildistillate boiling between C. and 330 C.

late boiling between 115 2. A process for separating mineral oilscontaining several hydrocarbon components having differentsolidification temperatures, comprising the steps of chilling said oilto a separation temperature between -20 C. and C. to solidify acomponent thereof, and separating said solidified component from acomponent having a lower solidification temperature in the presence ofseparating nitrogen bases separated from a mineral oil distillateboiling between 115 C. and 330 C.

3. A process for separating mineral oils containing several hydrocarboncomponents having different solidification temperatures, comprising thesteps of chilling said oil to a separation temperature to solidify acomponent thereof, and separating said solidified component from acomponent having a lower solidification temperature in the presence ofseparating diluent containing petroleum nitrogen bases separated from acracked mineral oil distillate boiling between 115 C. and 330 C.

4. A process for separating mineral oils containing several hydrocarboncomponents having different solidification temperatures, comprising thesteps of chillingsaid oil to a separation temperature to solidify acomponent thereof, and separating said solidified component from acomponent having a lower solidification temperature in the presence of adiluent mixture containing petroleum nitrogen bases separated from amineral oil distillate boiling between 115 C. and 330 C., and aselective solvent which has a relatively lower solvent power for saidcomponent having a lower solidification temperature and is completelymiscible with said petroleum nitrogen bases at said separationtemperatures.

5. The process according to claim 4 in which the selective solventcontains a nitrogen base consisting of a heterocyclic componentcontaining nitrogen in the ring and being free from alkyl side chainscontaining more than 2 carbon atoms.

6. A process for dewaxing wax-bearing mineral oils, comprising the stepsof chilling said oil to a dewaxing temperature to solidify wax, andseparating the wax from the oil in the presence of a dewaxing diluentcontaining petroleum nitrogen bases, separated from a mineral oildistil- C. and 330 C.

'7. The process according to claim 6 in which the petroleum nitrogenbases have been extracted so as to employ in the dewaxing operationsubstantially only those nitrogen bases which have dissociationconstants below 1x 10 8. A process for dewaxing wax-bearing mineraloils, comprising the steps of chilling said oil to a dewaxingtemperature to solidify wax, and separating the wax from the oil in thepresence of a dewaxing diluent containing petroleum nitrogen basesobtained by extracting a mineral oil distillate boiling between 115 C.and 330 C. with an acid.

9. A process for dewaxing wax-bearing mineral oils, comprising the stepsof chilling said oil to a dewaxing temperature to solidify wax, andseparating the wax from the oil in the presence' of a dewaxing diluentcontaining petroleum ni-' diluent containing petroleum trogen bases,separated from a. cracked mineral oil distillate boiling between 115 C.and 330 C.

10.A process for dewaxing wax-bearing mineral oils, comprising the stepsof chilling said oil a dewaxing temperature to solidify wax, andseparating the wax from the oil inthe presence of a dewaxing diluentmixture containing petroleum nitrogenbases, separated from a mineral oildistillate boiling between 115 C. and 330' O. and a selective dewaxingsolvent having a relatively lower solvent power for oil and completelymiscible with said petroleum nitrogen bases at said dewaxingtemperature.

11. A process for dewaxing wax-bearing mineral oils, comprising thesteps of chilling said oil to a dewaxing temperature to solidify wax,

.and separating the wax from the oil in thepresence of a dewaxingdiluent mixture containing petroleum nitrogen bases, separated" from acracked mineral oil distillate boiling between 115 C. and 330 C. and aselective dewaxing solvent having a relatively lower solvent power foroil and miscible in all proportions with said petroleum nitrogen basesat said dewaxing temperature. 1

12. 'I'heprocess according to claim 11 in which the selective dewaxingsolvent contains a nitrogen base consisting of a heterocyclic compoundcontaining nitrogen in the ring and being free from alkyl side chainscontaining more than two carbon atoms.

13. The process according to claim 11 in which the quantity of petroleumnitrogen bases is not substantially greater than that required to causethe oil and the diluents to exist as a single liquid I phase.

14. The process according to claim 11 in which the petroleum nitrogenbases have been extracted so as to employ in the dewaxing operationsubstantially only those nitrogen bases which have dissociationconstants lower than 1 10".

BERNARD SUTRO GREENSFELDER. MONROE EDWARD SPAGHT.

